1. Field of the Invention
The present invention relates to a reflective liquid crystal display apparatus of a front-lighting type.
2. Description of the Related Art
Conventional liquid crystal display apparatuses include a semitransparent type liquid crystal display apparatus having a back lighter. In such a liquid crystal display apparatus, light from the back lighter arranged behind the liquid crystal panel travels through a semitransparent reflector to the back side of the liquid crystal panel.
Recently, a semitransparent type liquid crystal display apparatus having a front lighter has been proposed. FIG. 11 illustrates an example of such a liquid crystal display apparatus. The liquid crystal display apparatus D includes a liquid crystal panel 41 which comprises a pair of transparent plates 40a, 40b, and liquid crystal C filled therebetween. The liquid crystal panel 41 has a front surface (upper surface in this figure) on which a first polarizer 43a and a light guide panel 42 are disposed, and a rear surface on which a second polarizer 43b and a reflector 44 are disposed.
The light guide panel 42 may be a transparent, generally planar plate, but has one surface which is formed with a plurality of projections 45. Each of the projections 45 is triangular, in cross section, including a first inclined surface 45a and a second inclined surface 45b which are different in the direction and angle of inclination. The projections 45, each of which extends in the widthwise direction of the light guide plate 42, are constantly spaced in a predetermined direction. Point light sources 46 are provided beside the light guide plate 42.
With the liquid crystal display apparatus D, when the light sources 46 are turned on to perform image display, light from the light sources 46 travels within the light guide panel 42 while being totally reflected by the inner surfaces of the projections 45 of the light guide panel 42. The light reflected by the projections 45 exits the light guide panel downwardly to enter the first polarizer 43a, the liquid crystal panel 41, and the second polarizer 43b, and is then reflected upwardly by the reflector 44. The light reflected by the reflector 44 travels again through the second polarizer 43b, the liquid crystal panel 41 and the first polarizer 43a to be emitted to the front side of the liquid crystal display apparatus D.
On the other hand, when image display is performed utilizing external light (e.g. sunlight or light from interior lighting) only, the external light travels downwardly to penetrate the light guide panel 42, the first polarizer 43a, the liquid crystal panel 41 and the second polarizer 43b. The light is then reflected by the reflector 44 upwardly to travel again through the second polarizer 43b, the liquid crystal panel 41, the first polarizer 43a and the light guide panel 42 to be emitted to the front side of the liquid crystal display apparatus D.
With the above-described liquid crystal display apparatus D in which the light guide panel 42 is formed with projections on its front surface, visibility of the display may often be deteriorated depending on the direction in which the user views the display. For example, in the case where the user views the liquid crystal panel 41 obliquely from the upper right in FIG. 11 (See an arrow E), external light impinging on the light guide panel 42 is partially reflected by the second inclined surfaces 45b of the projections 45 and then by the first inclined surfaces 45a to travel toward the user""s eyes.
Further, when the light sources 46 are turned on, light from the light sources 46 enters the light guide panel 42 to be totally reflected within the light guide panel 42. At that time, however, the light vertically impinging on the second inclined surfaces 45b is not totally reflected by the second inclined surfaces 45 but exits the light guide panel 42 to travel toward the user""s eyes. As a result, the contrast at the liquid crystal panel 41 is deteriorated, which leads to deteriorated visibility. Such a problem is peculiar to the liquid crystal display apparatus D which includes the light guide panel 42 formed with projections 45.
In the above-described liquid crystal display apparatus D, external light or light from the light sources 46 is utilized to view the liquid crystal panel 41, as described above. However, in the case where a mobile phone, for example, incorporating the liquid crystal display apparatus D is used utilizing sunlight and the user moves from a light place with sunlight to a dark place such as shade, it may be impossible to obtain sufficient light for visibility at the liquid crystal panel 41. Therefore, it is difficult for the user to view the letters or images displayed at the liquid crystal panel 41, so that the light sources 46 need to be turned on. In this way, the mobile phone incorporating the above-described liquid crystal display apparatus D is not conveniently usable.
It is therefore an object of the present invention to provide a liquid crystal display apparatus which is capable of eliminating or reducing the problems described above.
In accordance with a first aspect of the present invention, there is provided a liquid crystal display apparatus comprising: a liquid crystal panel; a transparent light guide panel disposed in front of the liquid crystal panel and having at least one irregular surface for emitting light entering from a light source toward the liquid crystal panel; and a reflector disposed behind the liquid crystal panel for reflecting light passing through the light guide panel and the liquid crystal panel toward the liquid crystal panel and the light guide panel; wherein the irregular surface of the light guide panel is partially formed with an absorbing layer for absorbing external light.
In the prior art structure which is not provided with an absorbing layer, external light may be reflected on the light guide panel to deteriorate the visibility depending on the direction in which the user views the liquid crystal panel. However, in accordance with the present invention, the light guide panel has a surface which is partially formed with an absorbing layer for absorbing external light. Therefore, the external light impinging on the absorbing layer of the light guide panel is absorbed by the layer without being reflected. Thus, the absorbing layer prevents the contrast deterioration to enhance the display quality of the liquid crystal panel.
Preferably, the irregular surface of the light guide panel may include a plurality of projections each of which is triangular in cross section with two inclined surfaces differing from each other in direction and angle of inclination, and the absorbing layer may be provided on a steeper inclined surface of each projection.
Preferably, the absorbing layer may be formed by applying a black coating onto the steeper inclined surface.
The steeper inclined surface of each said projection may be located farther away from the light source than the other inclined surface.
Alternatively, the steeper inclined surface of each said projection may be located closer to the light source than the other inclined surface.
Preferably, the irregular surface of the light guide panel may include a plurality of cylindrical projections each having a circumferential side surface on which the absorbing layer is formed.
The irregular surface of the light guide panel may be oriented away from the liquid crystal panel.
The irregular surface of the light guide panel may face toward the liquid crystal panel.
In accordance with a second aspect of the present invention, there is provided a liquid crystal display apparatus comprising a liquid crystal panel; a transparent light guide panel disposed in front of the liquid crystal panel and having at least one irregular surface for emitting light entering from a light source toward the liquid crystal panel; and a reflector disposed behind the liquid crystal panel for reflecting light passing through the light guide panel and the liquid crystal panel toward the liquid crystal panel and the light guide panel; wherein the irregular surface of the light guide panel is partially formed with a light storing layer for storing light.
With this structure, since the light guide panel 1 has a surface which is partially formed with a light storing layer, external light or light from the light source impinging on the light storing layer is stored at this layer. When the liquid crystal panel is used in a dark place with the light thus stored, the stored light is emitted from the light storing layer to illuminate the liquid crystal panel. Therefore, the letters or the image displayed on the liquid crystal panel can be viewed by the user. When the user moves from a light place to a dark place for example, the liquid crystal panel is illuminated with the light emitted from the light storing layer so that there is no need for turning on the light source. Therefore, a mobile phone for example may incorporate such a liquid crystal display apparatus for improving convenience of its use.
Preferably, the irregular surface of the light guide panel may include a plurality of projections each of which is triangular in cross section with two inclined surfaces differing from each other in direction and angle of inclination, and the light storing layer may be provided at a steeper inclined surface of each projection.
Preferably, the light storing layer may be formed by applying a light storing coating material onto the steeper inclined surface.
The light guide panel may have at least one side surface provided with a light storing layer.
The steeper inclined surface of each said projection may be located farther away from the light source than the other inclined surface.
Alternatively, the steeper inclined surface of each said projection may be located closer to the light source than the other inclined surface.
Preferably, the irregular surface of the light guide panel may include a plurality of cylindrical projections having a circumferential side surface on which the light storing layer is formed.
Preferably, the irregular surface of the light guide panel may be oriented away from the liquid crystal panel.
The irregular surface of the light guide panel may face toward the liquid crystal panel.
Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings.